`simd_div` and `simd_rem` ICEs for non-power-of-two length vectors on Aarch64

[calebzulawski]

For non-power-of-two length vectors on Aarch64 (#422):

• simd_div fails when the rhs argument is 0
• simd_rem fails when the rhs argument is MIN

These still need reproducers to submit to LLVM

[workingjubilee]

oh cool.

[workingjubilee]

@calebzulawski was this before we made our weird layout changes or just always

[workingjubilee]

also on what element types?

[calebzulawski]

Yeah, only with #[repr(simd, packed)]. I want to say it was for i8 but I don't remember for sure.